1. Field of the Invention
The present invention relates to a non-contact type profile measuring apparatus for irradiating parallel rays on a measurement object, thereby measuring the dimension of a generated shadow portion as the outside dimension of the measurement object.
2. Related Art
There is a non-contact type profile measuring apparatus having a laser and a polygon mirror in a light projecting section. A laser beam oscillated within a constant angle range by the polygon mirror passes through a mirror and a collimator lens to be changed into parallel rays. The parallel rays are irradiated on a measurement object, for example, a cylindrical and long object. Then the parallel rays including a shadow thereof are received by a light receiving element through a light receiving lens.
The light receiving element converts a light receiving signal including the shadow of the measurement object into an electric signal. The electric signal is sent to a signal processing section including a microprocessor. The signal processing section detects, through edge extraction, a portion corresponding to the shadow of the measurement object in the light receiving signal received by the light receiving element. Further, the signal processing section calculates the dimension of the shadow from a time of the edge extraction. A value thus obtained is displayed on a display section of the non-contact type profile measuring apparatus as a measurement result of the outside dimension of the measurement object.
In addition to the advantage that measuring precision is high, the non-contact type profile measuring apparatus using the laser has an advantage that a measured portion of the measurement object can be confirmed easily because the locus of the laser which can be visualized is described on the surface of the measurement object. With respect to the measuring apparatus, however, there is a problem in that the apparatus is expensive and the service life of the movable section for rotating the polygon mirror is undesirable.
There is another non-contact type profile measuring apparatus having a telecentric optical system. The telecentric optical system has such a structure that a diaphragm is provided in the focal position of a light receiving lens so that only parallel rays or components close thereto in a light which has passed through the light receiving lens pass through the diaphragm and then reach a one-dimensional image sensor.
According to such a structure, it is possible to use an inexpensive light source such as a light emitting diode or a lamp for a light projecting section in place of a laser. Moreover, deflecting means, such as a polygon mirror, is not required.
One of the drawbacks of the non-contact type profile measuring apparatus using the telecentric optical system, however, is that the measured portion of the measurement object is visualized with difficulty. In the system using the laser and the polygon mirror, the section of the parallel rays obtained by the collimator lens has a straight shape, and a locus thereof is described on the surface of the measurement object. Therefore, the measured portion can be visualized easily. In the telecentric optical system, however, the uniform section obtained by the collimator lens is almost circular. Therefore, it is hard to specify the measured portion even if a light source having a visable color is used.
In order to solve the problems described above, it is an object of the invention to provide a non-contact type profile measuring apparatus having a telecentric optical system, which easily specifies a measured portion of a measurement object.
The above-mentioned object can be achieved by a non-contact type profile measuring apparatus, according to the invention, comprising:
a converting section for converting a light transmitted from a light source into a light including a component parallel with an optical axis;
a light receiving lens for receiving a light including a shadow of a measurement object which is provided to intercept a part of the light;
a diaphragm provided in a rear side focal position of the light receiving lens;
a one-dimensional image sensor for receiving a light passing through the diaphragm;
a signal processing section for obtaining a dimension of the shadow of the measurement object as an outside dimension of the measurement object by processing an electric signal obtained from the one-dimensional image sensor;
a display section for displaying the outside dimension thus obtained;
a beam splitter provided on an optical path between the light receiving lens and the one-dimensional image sensor; and
a two-dimensional image sensor for receiving a light split by the beam splitter,
wherein the signal processing section processes an electric signal obtained from the two-dimensional image sensor, and the display section displays a monitor image including a measured portion of the measurement object. A light diffusing plate or a collimator lens may be used for the converting section for converting the light transmitted from the light source into the light including a component parallel with the optical axis. Alternatively, the surface of a lens of an LED to be used for the light source may be processed to have a diffusing function.
According to such a structure, the monitor image including the measured portion of the measurement object is displayed on the display section. Therefore, a user can easily specify the measured portion of the measurement object. The circular section of the parallel rays in the telecentric optical system having the light receiving lens and the diaphragm provided in the rear side focal position thereof, is a region to be displayed as the monitor image.
It is preferable that the beam splitter is provided between the diaphragm and the one-dimensional image sensor. Such an arrangement can be provided in a magnifying optical system capable of increasing a distance between the diaphragm and the one-dimensional image sensor. An advantage of the present invention is that a diaphragm is not required for an optical path from the beam splitter to the two-dimensional image sensor.
In the case in which the beam splitter is provided between the light receiving lens and the diaphragm, a second diaphragm is further provided in a second rear side focal position of the light receiving lens formed between the beam splitter and the two-dimensional image sensor. By decreasing the distance between the diaphragm and the one-dimensional image sensor to obtain a reducing optical system, it is possible to obtain the advantage wherein the optical system can be of a smaller size.
The distance is generally based on the available range of the beam splitter. Therefore, compared with the beam splitter provided between the diaphragm and the one-dimensional image sensor, the distance between the diaphragm and the one-dimensional image sensor in the case where the beam splitter is provided between the light receiving lens and the diaphragm, can be decreased by the available range of the beam splitter. One example of the decreasable distance is basically a range of from 10mm to 100mm, although the distance depends on device size and the like.
Further, it is preferable that the signal processing section obtains a measuring line corresponding to the measured portion of the measurement object from which the one-dimensional image sensor receives the light, and the display section displays the measuring line so that it is superposed on the monitor image of the measurement object. Consequently, the user can specify the measured portion of the measurement object more accurately. A method of controlling the display position of the measuring line which is to be carried out before the shipment of the profile measuring apparatus will be described below.
Furthermore, it is preferable that the signal processing section obtains a mark indicative of an edge position of the shadow of the measurement object by processing the electric signal obtained from the one-dimensional image sensor, and the display section displays the mark so that it is superposed on the monitor image of the measurement object. Consequently, the user can visually confirm a portion (edge position) measured as the outside dimension (from an edge to an edge) in the measured portion (measuring line) of the measurement object. A method of controlling the relationship between the mark display of the edge position and the monitor image which is to be carried out before the shipment of the measuring apparatus will be described below.
As described above, according to the non-contact type profile measuring apparatus having the telecentric optical system of the invention, the monitor image including the measured portion of the measurement object is displayed on the display section. Therefore, a user can easily specify the measured portion of the measurement object. Moreover, the measuring line indicative of the measured portion measured by the one-dimensional image sensor and the mark indicative of the edge position on the measuring line are displayed on the display section so that they are superposed on the monitor image. Therefore, in the case in which the outside dimension of the particular portion of the measurement object is measured, it is possible to accurately position the measurement object in such a manner that the shift or inclination of the measurement object is not caused while watching the monitor image.